The invention relates to an incident light, bright-field, Kohler illuminating device for microscopes which reflects an illuminating beam into one half of the pupil of a microscope objective.
In the reference work "ABC's of Optics" by K. Mutze, Werner Dausin Press, Hanau (1961), illuminating devices of the aforementioned type are described and illustrated on pages 560-561. The device most like the invention is designated as a prism illuminator. The illuminating light is reflected from the hypotenuse of a rectangular prism toward the objective and passed through the objective onto the object. The prism covers half of the exit pupil. Imaging of the object is effected through the other half of the exit pupil. In order to prevent vignetting of the field of vision, the prism must be located, insofar as possible, in the exit pupil of the objective. Consequently, the incident light, bright-field objectives are formed especially short.
Illuminating devices of this type have the advantage of almost complete utilization of the reflected illuminating light. They may be used for a strictly Kohler type illumination, in which a luminous-field diaphragm is imaged in the object plane and an aperture diaphragm is imaged in the exit pupil of the microscope objective. If a so-called Berek prism is used, polar incident light illumination is also possible. A disadvantage, on the other hand, consists of the short distance of the prism from the objective required for the satisfactory imaging of the object; which makes a special design of the microscope stand necessary. Interchangeable illuminating devices of this type are usually found only in microscopes with individually interchangeable objectives and not with revolvably changeable objectives. It is not possible to subsequently equip a transmitted light microscope with such an illuminating device.